GreaseMonkey Addon is disable after I did enable it and then restarted Mozilla Firefox. Why?

First day, I installed GreaseMonkey and it is ok and works. And Second day, I open MF(Mozilla Firefox),
It asks me to enable GreaseMonkey. I make it enable and it says it needs to restart MF.
I restart MF but it also asks me to enable GM again.

First day, I installed GreaseMonkey and it is ok and works. And Second day, I open MF(Mozilla Firefox),
It asks me to enable GreaseMonkey. I make it enable and it says it needs to restart MF.
I restart MF but it also asks me to enable GM again.

If you see disabled or not compatible extensions in "Firefox/Tools > Add-ons > Extensions" then click the Tools button at the left end side of the Search Bar ("Find Updates" button in older Firefox versions) to check if there is a compatibility update available.

It is possible that there is a problem with the file(s) that store the extensions registry.
Delete the extensions.* files (e.g. extensions.sqlite, extensions.ini) and compatibility.ini in the Firefox profile folder to reset the extensions registry.
*https://support.mozilla.org/kb/Profiles
New files will be created when required.
See "Corrupt extension files":
*http://kb.mozillazine.org/Unable_to_install_themes_or_extensions
*https://support.mozilla.org/kb/Unable+to+install+add-ons
If you see disabled or not compatible extensions in "Firefox/Tools > Add-ons > Extensions" then click the Tools button at the left end side of the Search Bar ("Find Updates" button in older Firefox versions) to check if there is a compatibility update available.
If this hasn't helped then also delete the addons.sqlite file.
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See also:
*http://kb.mozillazine.org/Preferences_not_saved